Conventionally, for example, a movable magnet-type instrument (see, for example, Patent Document 1) provided with a magnet rotor, which operates upon energization of a coil, or an instrument (see, for example, Patent Document 2) rotationally supported with the use of a stepping motor, which comprises a magnet rotor supported rotatably in a stator, is adopted as, for example, an instrument for vehicles.    Patent Document 1: JP-A-2001-289876    Patent Document 2: JP-A-2001-317970
As a conventional magnet rotor used for a movable magnet-type instrument, a stepping motor, etc., with a view to miniaturization and lightening, a rotor body made of a plastic material is integrally and coaxially formed in a hollow of an annularly molded magnet by means of insert-molding or the like to constitute a magnet rotor.